How to Bleed
FAQ and Step-by-Step Instructions
by Dave Zeckhausen
How often should
you bleed your brakes?
specify that brakes should be bled every two years, starting from the date
the vehicle was built. For race cars, it may be necessary to bleed the
brakes before each track event or, if the pedal becomes soft during an event, to bleed between sessions. If you find yourself
needing to bleed the brakes between sessions, it's time to switch to a brake fluid
with a higher boiling point, such as
AP Racing PRF, Brembo LCF600, or even Castrol SRF.
Why bleed brakes?
Fresh brake fluid
has a significantly higher boiling point than old fluid, allowing harder braking without
fade. This is because brake fluid is hygroscopic and readily absorbs
moisture. The more moisture in the fluid, the lower the boiling
That same moisture promotes corrosion. Frequent bleeding with
fresh fluid allows brake components to last longer. A well
maintained brake system can help you avoid ever having to replace calipers,
master cylinder or an expensive ABS control unit.
bleeding process, done properly, removes air bubbles from the hydraulic
system, resulting in firmer brake pedal feel and more linear, responsive
braking performance. Too much air in the system can be dangerous
and result in the pedal sinking to the
floor. Air is compressible, brake fluid is not.
How much brake
fluid is required?
It is usually
possible to bleed all four corners of the car with somewhere between 1/2 and one liter
of brake fluid. If you've just installed new brake lines or a big
brake kit, it may require more fluid, especially if you are a novice at
Must brakes be bled in a specific order?
Bleeding is done one
wheel at a time. The "old timers" will tell you to start with the
wheel furthest from the master cylinder and work your way closer.
Typically, this would mean RR, LR, RF, then LF. However, it doesn't
really matter if you start with the front or rear wheels, since they are on
separate circuits on modern cars with ABS and/or dynamic stability
How are brakes bled?
There are many
techniques for bleeding brakes and lots of gadgets to make the job easier.
replacing old fluid with new, many of these techniques work fine. But
for removing air bubbles from the system, one approach is superior.
That is the "old fashioned method", which requires an assistant to push on the
brake pedal while the mechanic opens and closes the bleed valve on the
calipers. This 2-person method generates a sufficient jolt to the
brake fluid to knock loose pesky bubbles and allows them to be flushed
away. By following these instructions, you will be more likely to end
up with a firm brake pedal, often with better feel than the day your car
rolled off the assembly line.
Working on your own car can be dangerous. Even quality jack stands can
collapse if not positioned properly, and a floor jack can fail suddenly and
without warning. You can be seriously injured or even killed if you do not
follow proper safety procedures. Zeckhausen Racing LLC assumes no
liability expressed or implied for the improper use of these instructions.
Block a front wheel
with a piece of wood to prevent the car from rolling. Raise the back
of the car with a floor jack and then lower it onto a pair of jackstands.
Remove the rear
Open the brake fluid
remove as much old brake fluid as possible, using a
suction tool or a turkey baster. Be careful not to spill any fluid, as
it will dissolve the paint on your car.
Fill the brake
reservoir to the top with fresh fluid.
Place a box end
wrench over the bleed screw on the right rear caliper. Push a clear
plastic tube over the nipple on the bleed screw and place the opposite end
into a catch bottle. Auto parts stores sell nice catch bottles with a cover
that prevents fluid from spilling if it tips over, a 1-way check valve in
the cap, and a rubber fitting on the caliper end of the plastic line that
snaps in place over a wide range of bleed screw nipple sizes.
Tell your assistant
to pump the brake pedal a few times until it becomes firm. This is
especially important if you have just replaced pads. If you've
installed new stainless braided brake lines or installed a big brake kit,
there may be enough air in the system that the brake pedal will not get
firm. That's OK. Just move on to the next step.
Tap the caliper a few
times with a rubber mallet or "dead-blow" hammer. This helps to knock
loose air bubbles that may
be clinging to inside surfaces of the caliper.
Have your assistant
PUSH hard on the brake pedal and HOLD. With a quick motion, open the
bleed screw about 1/4 turn. Fluid (and probably a few air bubbles)
will flow through the plastic tube and into the catch bottle. A light
placed behind the tube will make it easier to see what is coming out of the
Close the bleed screw
just before the brake pedal reaches the floor. Don't worry if the
timing is off at first. You will quickly figure it out with feedback
from your assistant.
Tell your assistant
Repeat steps 8 - 10. Do this about 6 times and then go to the front of
the car to check the fluid level. You MUST NOT allow the level to fall to the point where you
into the master cylinder.
Top off the brake
fluid level and continue for a total of about 10 pumps or until you no
longer see any air bubbles coming out of the caliper.
Repeat the process
for the other rear caliper.
Make sure both
calipers are wiped clean of brake fluid and that none has spilled on the
rotors or pads. Use brake cleaning spray if necessary. Reinstall
the rear wheels and torque to factory specification, then lower car to the
Now apply the parking
brake, put the car in gear (or PARK) and raise the front of the car with
your floor jack. Lower it onto a pair of jackstands.
Remove the front
Follow the exact same
technique as with the rear wheels, starting with the passenger side caliper.
The fluid will flow more rapidly out of the front calipers, so you will need
to check the level in the brake fluid reservoir more frequently to avoid
letting it drop too low.
Reinstall and torque
the front wheels, then lower the car to the ground.
Top off the brake
fluid reservoir and replace the cap.